Tunable filter arrangement

ABSTRACT

The invention describes a tunable filter arrangement with at least two resonators which are coupled to one another and of which at least one is connected to a capacitor with tunable capacitance. The electrical properties of the resonator, and thus the overall filter characteristic, can be changed through a change in the capacitance of the capacitor.  
     Furthermore, a transmitter, a receiver, a mobile telephone device, and a wireless data transmission system comprising such a filter arrangement are disclosed, as is a tunable bulk acoustic wave resonator.

[0001] The invention relates to a tunable filter arrangement. Theinvention further relates to a transmitter, a receiver, a mobiletelephone device, and a cordless data transmission system with a tunablefilter arrangement, as well as to a tunable bulk acoustic waveresonator.

[0002] The stormy developments in the field of mobile telephony and thecontinuous miniaturization of cordless telephone devices lead to higherrequirements being imposed on the individual components. Thus a highselectivity in the high frequency part is necessary for protecting thereceiver from the rising number of potentially interfering signals fromother systems. This is achieved, for example, by means of bandpassfilters which transmit only a limited frequency band and which suppressall frequencies above and below this band.

[0003] At the present moment, filters with ceramic electromagneticresonators are among the means used for this purpose. A miniaturizationof these filters, however, is limited by the electromagnetic wavelength.So-called surface acoustic wave (SAW) filters built up from surfaceacoustic wave resonators can be given a considerably smallerconstruction. This is because the acoustic wavelength is smaller thanthe electromagnetic wavelength by 4 to 5 orders of magnitude. A surfaceacoustic wave resonator comprises a piezoelectric layer on whichfinger-shaped electrodes are provided. A signal applied to the inputelectrodes excites the piezoelectric material into mechanicalvibrations, which propagate in the form of acoustic waves on the upperside of the layer and are converted back into an electric signal againby the output electrodes.

[0004] An alternative is formed by bulk acoustic wave (BAW) filterscomprising bulk acoustic wave resonators. Bulk acoustic wave filtershave advantages as regards their size, power, and IC compatibility. Bulkacoustic wave resonators are built up from three components inprinciple. The first component generates the acoustic wave and comprisesa piezoelectric layer. Two electrodes arranged above and below thepiezoelectric layer represent the second component. The third componenthas the task of acoustically insulating the substrate from thevibrations generated by the piezoelectric layer.

[0005] It is an interesting aspect that the properties of a resonator orfilter can be varied. This may be done, for example, through coupling ofa resonator or filter with a varicap diode. It is a disadvantage of thecombination of active and passive components that the active componentsmay be contaminated by the materials of the passive components duringthe manufacture of the resonator or filter.

[0006] An alternative possibility is disclosed in U.S. Pat. No.5,446,306. This describes a semiconductor bulk acoustic wave resonatorand a semiconductor bulk acoustic wave filter which comprises asemiconducting substrate, a first and second electrode, and arrangedtherebetween a piezoelectric layer of AlN or ZnO. The resonancefrequency of the resonator is changed in that a DC voltage is applied tothe electrodes.

[0007] The invention has for its object to provide a tunable filterarrangement which can be manufactured in a simple and inexpensivemanner.

[0008] This object is achieved by means of a tunable filter arrangementwhich comprises a substrate and provided thereon an arrangement of atleast two mutually coupled resonators of which at least one is connectedto a capacitor with tunable capacitance.

[0009] The electrical properties of the resonator, for example itsresonance frequency or its anti-resonance frequency, can be changedthrough coupling of a resonator to a capacitor. If the resonator ispresent in a filter arrangement, these changes will influence theoverall filter characteristic. Since the capacitor has a tunable, i.e.changeable capacitance value, these changes can be effected more or lessstrongly.

[0010] It is preferred that the capacitor comprises a dielectric of amaterial having a voltage-dependent relative dielectric constant ε_(r).

[0011] Certain materials have a dielectric constant ε which is stronglydependent on an applied voltage. When a DC voltage is applied to thefirst and the second electrode of a capacitor having a dielectric with avoltage-dependent relative dielectric constant ε_(r), the value of thedielectric constant ε_(r) will drop, and thus the capacitance of thecapacitor. This also changes the influence of the capacitor on theelectrical properties of the resonator to which it is coupled.

[0012] It is particularly highly preferred that the material with avoltage-dependent relative dielectric constant ε_(r) is chosen from thegroup comprising PbTi_(1−x)Zr_(x)O₃ (0≦x≦1) with and without dopants ofLa, Nb or Mn with and without excess lead, BaTiO₃ with and withoutdopants, SrTiO₃ with and without dopants, Ba_(1−x)Sr_(x)TiO₃ (0≦x≦1)with and without dopants of Ca and Pb, Ba_(1−x)Sr_(x)TiO₃ (0≦x≦1)+MgO,Ba_(1−x)Sr_(x)TiO₃—Pb_(1−y)Ca_(y)TiO₃ (0≦x≦1, 0≦y≦1), CaTiO₃ doped withBi, Sr_(n+1)Ti_(n)O_(3n+1) (1≦n≦5), Pb_(1−x)Ca_(x)TiO₃ (0≦x≦1),Ba_(1−x)Sr_(x)TiO₃ (0≦x≦1) with and without added VO_(x) (1≦x≦2.5)and/or SiO₂, Ba_(1−x)Sr_(x)Zr_(y)Ti_(1−y)O₃ (0≦x≦1, 0≦y≦1) with andwithout dopants, Ba_(1−x)Pb_(x)TiO₃ (0≦x≦1) with and without excesslead, Ba_(1−x)Ca_(x)TiO₃ (0≦x≦1), SrZr_(x)Ti_(1−x)O₃ (0≦x≦1) with andwithout dopants, [PbMg_(⅓)Nb_(⅔)O₃]_(x)—[PbTiO₃]_(1−x) (0≦x≦1),(Pb,Ba,Sr)(Mg_(⅓)Nb_(⅔))_(x)Ti_(y)(Zn_(⅓)Nb_(⅔))_(1−x-y)O₃ (0≦x≦1,0≦y≦1), Pb_(1−x)Ca_(x)TiO₃ (0≦x≦1),(Ba_(1−x+y/8)Sr_(x+y/8))₂Na_(1−y)Nb₅O₁₅ (0≦x≦1, 0≦y≦1) with and withoutexcess Na⁺, (Ba_(1−x+y/8)Sr_(x+y/8))₂K_(1−y) Nb₅O₁₅ (0≦x≦1, 0≦y≦1) withand without excess K⁺, (Ba_(1−x)Sr_(x))₂K_(1−3y)SE_(y)Nb₅O₁₅ (0≦x≦1,0≦y≦1, SE=ion from the group of rare earths), Sr₂Ba₄Ti₂Nb₈O₃₀, BiNbO₄with and without VO_(x) (1≦x≦2.5) and/or CuO dopants,(Bi_(2−x)Zn_(x))(Nb_(2−y)Zn_(y))O_(x),

[0013] Bi₂(Zn_(⅓)Nb_(⅔))₂O₇,

[0014] a) Pb(Mg_(½)WI_(½))O₃,

[0015] b) Pb(Fe_(½)Nb_(½))O₃,

[0016] c) Pb(Fe_(⅔)WI_(⅓))O₃,

[0017] d) Pb(Ni_(⅓)Nb_(⅔))O₃,

[0018] e) Pb(Zn_(⅓)Nb_(⅔))O₃,

[0019] f) Pb(Sc_(½)Ta_(½))O₃,

[0020] combinations of the compounds a) to f) with PbTiO₃ and/orPb(Mg_(⅓)Nb_(⅔))O₃ with and without excess lead and Ba_(1−x)Zr_(x)TiO₃(0≦x≦1).

[0021] These materials show a particularly strong dependence of theirdielectric constants ε on an applied voltage.

[0022] It is preferred that the resonators are chosen from the groupcomprising bulk acoustic wave resonators, surface acoustic waveresonators, and LC resonators.

[0023] Filter arrangements comprising bulk acoustic wave resonators orsurface acoustic wave resonators can be manufactured with a high qualityfactor Q and a high coupling factor k. LC resonators can be manufacturedin a simple manner.

[0024] It is particularly preferred that the resonators are constructedin a thin-film technology process.

[0025] A construction of the resonators in thin-film technology on asubstrate renders it possible to obtain such a filter arrangement withsmall dimensions.

[0026] It is particularly highly preferred that a bulk acoustic waveresonator comprises a resonator unit of a lower and an upper electrodeas well as a piezoelectric layer arranged therebetween and a reflectionelement arranged between the substrate and the resonator unit.

[0027] Such a bulk acoustic wave resonator can be manufactured withoutcumbersome lithographic processes because the resonance frequency of theresonator is defined by the layer thickness of the piezoelectric layer.In addition, such a bulk acoustic wave resonator is clearly more robustthat other types of bulk acoustic wave resonators such as single-crystalresonators, resonators with membranes, or resonators with an air gap.

[0028] In a preferred embodiment, the resonator connected to a capacitorof tunable capacitance is also connected to a further capacitor.

[0029] It is particularly highly preferred in this embodiment that atleast one capacitor is connected in series with and at least onecapacitor is connected in parallel to the resonator.

[0030] This embodiment offers a particularly wide range of possibilitiesfor varying the filter characteristic.

[0031] The invention furthermore relates to a transmitter, a receiver, amobile telephone device, and a wireless data transmission systemprovided with a tunable filter arrangement which comprises a substrateand provided thereon an arrangement of at least two mutually coupledresonators of which at least one is connected to a capacitor withtunable capacitance.

[0032] The invention furthermore relates to a tunable bulk acoustic waveresonator which comprises a substrate and provided thereon a resonatorunit with a lower and an upper electrode as well as a piezoelectriclayer arranged therebetween, and a reflection element which is arrangedbetween the substrate and the resonator unit, which resonator isconnected to a capacitor having a tunable capacitance value.

[0033] The electrical properties of the bulk acoustic wave resonator canbe trimmed over a wide range through coupling of the resonator to atunable capacitor.

[0034] The invention will now be explained in more detail below withreference to two Figures and four embodiments, with

[0035]FIG. 1 showing a bulk acoustic wave resonator of a tunable filterarrangement connected to two capacitors in cross-section,

[0036]FIG. 2 showing the circuit diagram of an embodiment of a tunablefilter arrangement,

[0037]FIG. 3 being a plan view of a tunable filter arrangement with acircuit arrangement in accordance with FIG. 2, and

[0038]FIG. 4 showing the filter curve of a tunable filter arrangement.

[0039] In FIG. 1, a tunable filter arrangement comprises a substrate 1which comprises, for example, a ceramic material, a ceramic materialwith a glass planarizing layer, a glass-ceramic material, a glassmaterial, Si, GaAs, or sapphire. If silicon or GaAs is used as thesubstrate 1, an additional passivating layer, for example made of SiO₂or glass, is provided. On the substrate 1 there is a reflection element2 which is formed by a layer of an acoustically reflecting substancefrom the group of polymers and porous substances. The acousticallyreflecting substance used may be, for example, an aerogel, a xerogel, aglass foam, a foam-type adhesive, a foamed synthetic resin, or asynthetic resin of low density. The aerogel used may be, for example, aninorganic aerogel composed of silica gel or porous SiO₂ structures, oran organic aerogel such as, for example, a resorcin-formaldehydeaerogel, a melamine-formaldehyde aerogel, or a phenol-formaldehydeaerogel. The xerogel used may be, for example, an inorganic xerogel suchas highly condensed polysilicic acid or an organic xerogel such as glueor agar-agar. Foamed substances used may be, for example, chemically orphysically foamed polymers such as, for example, polystyrol,polycarbonate, polyvinyl chloride, polyurethane, polyisocyanate,polyisocyanurate, polycarbodiimide, polymethacrylimide, polyacrylimide,acryl-butadiene-styrol copolymers, polypropylene, or polyester. Inaddition, foamed synthetic resins such as, for example,phenol-formaldehyde resins or furane resins having a high porosity owingto carbonatization may be used. The synthetic resin of low density usedmay be, for example, a cross-linked polyvinyl ether, a cross-linkedpolyaryl ether, polytetrafluoroethylene, poly(p-xylylene),poly(2-chloro-p-xylylene), poly(dichloro-p-xylylene),polybenzocyclobutene, a styrol-butadiene copolymer, anethylene-vinyl-acetate polymer, or an organic siloxane polymer.Resonator units and capacitor units are provided on the reflectionelement 2. A resonator unit comprises a first electrode 5, apiezoelectric layer 6, and a second electrode 7. The electrodes 5 and 7are preferably made from a well conducting material of low acousticdamping and may comprise, for example, Ag_(1−x)Pt_(x) (0≦x≦1), Pt with alayer thickness from 50 nm to 1 μm, Ti with a layer thickness from 1 to20 nm/Pt with a layer thickness from 20 to 600 nm, Ti with a layerthickness from 1 to 20 nm/Pt with a layer thickness from 20 to 600 nm/Tiwith a layer thickness from 1 to 20 nm, Pt with a layer thickness from20 to 600 nm/Ti with a layer thickness from 1 to 20 nm, Al, Al dopedwith Cu, Al doped with Si, Al doped with Mg, W, Ni, Mo, Au, Cu,Ti/Pt/Al, Ti/Ag, Ti/Ag/Ti, Ti/Ag/Ir, Ti/Ir, Ti/Pd, Ti/Ag_(1−x)Pt_(x)(0≦x≦1), Ti/Ag_(1−x)Pd_(x) (0≦x≦1), Ti/Pt_(1−x)Al_(x) (0≦x≦1),Pt_(1−x)Al_(x) (0≦x≦1), Ti/Ag/Pt_(1−x)Al_(x) (0≦x≦1), Ti/Ag/Ru,Ti/Ag/Ir/IrO_(x) (0≦x≦2), Ti/Ag/Ru/RuO_(x) (0≦x≦2),Ti/Ag/Ru/Ru_(x)Pt_(1−x) (0≦x≦1), Ti/Ag/Ru/Ru_(x)Pt_(1−x)/RuO_(y) (0≦x≦1,0≦y≦2), Ti/Ag/Ru/RuO_(x)/Ru_(y)Pt_(1−y) (0≦x≦2, 0≦y≦1),Ti/Ag/Ru_(x)Pt_(1−x) (0≦x≦1), Ti/Ag/Pt_(x)Al_(1−x) (0≦x≦1),Pt_(x)Al_(1−x)/Ag/Pt_(y)Al_(1−y) (0≦x≦1, 0≦y≦1),Ti/Ag/Pt_(y)(RhO_(x))_(1−y) (0≦x≦2, 0≦y≦1), Ti/Ag/Rh/RhO_(x) (0≦x≦2),Ti/Ag/Pt_(x)Rh_(1−x) (0≦x≦1), Ti/Ag/Pt_(y)(RhO_(x))_(1−y)/Pt_(z)Rh_(1−z)(0≦x≦2, 0≦y≦1, 0≦z≦1), Ti/Ag_(x)Pt_(1−x)/Ir (0≦x≦1),Ti/Ag_(x)Pt_(1−x)/Ir/IrO_(y) (0≦x≦1, 0≦y≦2),Ti/Ag_(x)Pt_(1−x)/Pt_(y)Al_(1−y) (0≦x≦1, 0≦y≦1), Ti/Ag_(x)Pt_(1−x)/Ru(0≦x≦1), Ti/Ag_(x)Pt_(1−x)/Ru/RuO_(y) (0≦x≦1, 0≦y≦2), Ti/Ag/Cr,Ti/Ag/Ti/ITO, Ti/Ag/Cr/ITO, Ti/Ag/ITO, Ti/Ni/ITO, Ti/Rh, Ti/Ru, Rh,Rh/RhO₂, Ti/Ni/Al/ITO, Ti/Ni, Ti/W/Ti, W_(x)Ti_(1−z) (0≦x≦1),W_(x)Ti_(1−x)/Al(Cu) (0≦x≦1), W_(x)Ti_(1−x)/Al(Si) (0≦x≦1),W_(x)Ti_(1−x)/Al (0≦x≦1) or Ti/Cu. The material for the piezoelectriclayer 6 may be chosen, for example, from the group of AlN, ZnO,PbTi_(1−x)Zr_(x)O₃ (0≦x≦1) with and without dopants of La or Mn, LiNbO₃,LiTaO₃, PbNb₂O₆, Pb_(1−x)Ca_(x)TiO₃ (0≦x≦1),[Pb(Mg_(⅓)Nb_(⅔))O₃]—[PbTiO₃]_(1−x) (0≦x≦1), BaTiO₃, K_(1−x)Na_(x)NbO₃(0≦x≦1), (Cd,Na)NbO₃, (Bi,Na)TiO₃, (Bi,Na,Pb,Ba)TiO₃, Bi₇Ti₄NbO₂₁,(Ba_(1−x)Sr_(x))₂NaNb₅O₁₅ (0≦x≦1), (Ba_(1−x)Sr_(x))₂KNb₅O₁₅ (0≦x≦1),

[0040] a) Pb(Mg_(½)WI_(½))O₃,

[0041] b) Pb(Fe_(½)Nb_(½))O₃,

[0042] c) Pb(Fe_(⅔)WI_(⅓))O₃,

[0043] d) Pb(Ni_(⅓)Nb_(⅔))O₃,

[0044] e) Pb(Zn_(⅓)Nb_(⅔))O₃,

[0045] f) Pb(Sc_(½)Ta_(½))O₃,

[0046] combinations of the compounds a) to f) with PbTiO₃ andPb(Mg_({fraction (13)})Nb_(⅔))O₃ with and without excess lead, andpolyvinylidene fluoride (PVDF).

[0047] Two capacitors CA and CB are provided on the reflection element 2in the vicinity of the resonator units. The capacitor CA has a tunablecapacitance and comprises a dielectric 8 of a material which has avoltage-dependent relative dielectric constant ε_(r). The capacitorC_(B) need not necessarily have a tunable capacitance and comprises thedielectric 4.

[0048] The electrodes 5 and 7 of the resonator unit may be structuredsuch that they each at the same time form an electrode of one of thecapacitors C_(A) and C_(B).

[0049] Thus, for example, the electrode 7 may be structured such that italso forms the lower electrode of the capacitor C_(A) with tunablecapacitance. A dielectric 8 is provided on the lower electrode of thecapacitor C_(A), and an upper electrode 9 is provided on the dielectric8 so as to form the upper electrode 9 of the capacitor C_(A). Thedielectric 8 comprises a material with a voltage-dependent relativedielectric constant ε_(r) such as, for example, PbTi_(1−x)Zr_(x)O₃(0≦x≦1) with and without dopants of La, Nb or Mn with and without excesslead, BaTiO₃ with and without dopants, SrTiO₃ with and without dopants,Ba_(1−x)Sr_(x)TiO₃ (0≦x≦1) with and without dopants of Ca and Pb,Ba_(1−x)Sr_(x)TiO₃ (0≦x≦1)+MgO, Ba_(1−x)Sr_(x)TiO₃—Pb_(1−y)Ca_(y)TiO₃(0≦x≦1, 0≦y≦1), CaTiO₃ doped with Bi, Sr_(n+1)Ti_(n)O_(3n+1) (1≦n≦5),Pb_(1−x)Ca_(x)TiO₃ (0≦x≦1), Ba_(1−x)Sr_(x)TiO₃ (0≦x≦1) with and withoutadded VO_(x) (1≦x≦2.5) and/or SiO₂, Ba_(1−x)Sr_(x)Zr_(y)Ti_(1−y)O₃(0≦x≦1, 0≦y≦1) with and without dopants, Ba_(1−x)Pb_(x)TiO₃ (0≦x≦1) withand without excess lead, Ba_(1−x)Ca_(x)TiO₃ (0≦x≦1), SrZr_(x)Ti_(1−x)O₃(0≦x≦1) with and without dopants, [PbMg_(⅓)Nb_(⅔)O₃]_(x)—[PbTiO₃]_(1−x)(0≦x≦1), (Pb,Ba,Sr)(Mg_(⅓)Nb_(⅔))_(x)Ti_(y)(Zn_(⅓)Nb_(⅔))_(1−x-y)O₃(0≦x≦1, 0≦y≦1), Pb_(1−x)Ca_(x)TiO₃ (0≦x≦1),(Ba_(1−x+y/8)Sr_(x+y/8))₂Na_(1−y)Nb₅O₁₅ (0≦x≦1, 0≦y≦1) with and withoutexcess Na⁺, (Ba_(1−x+y/8)Sr_(x+y/8))₂K_(1−y) Nb₅O₁₅ (0≦x≦1, 0≦y≦1) withand without excess K⁺, (Ba_(1−x)Sr_(x))₂K_(1−3y)SE_(y)Nb₅O₁₅ (0≦x≦1,0≦y≦1, SE=ion from the group of rare earths), Sr₂Ba₄Ti₂Nb₈O₃₀, BiNbO₄with and without VO_(x) (1≦x≦2.5) and/or CuO dopants,(Bi_(2−x)Zn_(x))(Nb_(2−y)Zn_(y))O_(x),

[0050] Bi₂(Zn_(⅓)Nb_(⅔))₂O₇,

[0051] a) Pb(Mg_(½)WI_(½))O₃,

[0052] b) Pb(Fe_(½)Nb_(½))O₃,

[0053] c) Pb(Fe_(⅔)WI_(⅓))O₃,

[0054] d) Pb(Ni_(⅓)Nb_(⅔))O₃,

[0055] e) Pb(Zn_(⅓)Nb_(⅔))O₃,

[0056] f) Pb(Sc_(½)Ta_(½))O₃,

[0057] combinations of the compounds a) to f) with PbTiO₃ and/orPb(Mg_(⅓)Nb_(⅔))0 ₃ with and without excess lead and Ba_(1−x)Zr_(x)TiO₃(0≦x≦1).

[0058] The electrode 9 of the capacitor CA may comprise, for example,Ag_(1−x)Pt_(x) (0≦x≦1), Pt with a layer thickness of 50 nm to 1 μm, Tiwith a layer thickness from 1 to 20 nm/Pt with a layer thickness from 20to 600 nm, Ti with a layer thickness from 1 to 20 nm/Pt with a layerthickness from 20 to 600 nm/Ti with a layer thickness from 1 to 20 nm,Pt with a layer thickness from 20 to 600 nm/Ti with a layer thicknessfrom 1 to 20 nm, W, Ni, Mo, Au, Cu, Ti/Pt/Al, Ti/Ag, Ti/Ag/Ti, Ti/Ag/Ir,Ti/Ir, Ti/Pd, Ti/Ag_(1−x)Pt_(x) (0≦x≦1), Ti/Ag_(1−x)Pd_(x) (0≦x≦1),Ti/Pt_(1−x)Al_(x) (0≦x≦1), Pt_(1−x)Al_(x) (0≦x≦1), Ti/Ag/Pt_(1−x)Al_(x)(0≦x≦1), Ti/Ag/Ru, Ti/Ag/Ir/IrO_(x) (0≦x≦2), Ti/Ag/Ru/RuO_(x) (0≦x≦2),Ti/Ag/Ru/Ru_(x)Pt_(1−x) (0≦x≦1), Ti/Ag/Ru/Ru_(x)Pt_(1−x)/RuO_(y) (0≦x≦1,0≦y≦2), Ti/Ag/Ru/RuO_(x)/Ru_(y)Pt_(1−y) (0≦x≦2, 0≦y≦1),Ti/Ag/Ru_(x)Pt_(1−x) (0≦x≦1), Ti/Ag/Pt_(x)Al_(1−x) (0≦x≦1),Pt_(x)Al_(1−x)/Ag/Pt_(y)Al_(1−y) (0≦x≦1, 0≦y≦1),Ti/Ag/Pt_(y)(RhO_(x))_(1−y) (0≦x≦2, 0≦y≦1), Ti/Ag/Rh/RhO_(x) (0≦x≦2),Ti/Ag/Pt_(x)Rh_(1−x) (0≦x≦1), Ti/Ag/Pt_(y)(RhO_(x))_(1−y)/Pt_(z)Rh_(1−z)(0≦x≦2, 0≦y≦1, 0≦z≦1), Ti/Ag_(x)Pt_(1−x)/Ir (0≦x≦1),Ti/Ag_(x)Pt_(1−x)/Ir/IrO_(y) (0≦x≦1, 0≦y≦2),Ti/Ag_(x)Pt_(1−x)/Pt_(y)Al_(1−y) (0≦x≦1, 0≦y≦1), Ti/Ag_(x)Pt_(1−x)/Ru(0≦x≦1), Ti/Ag_(x)Pt_(1−x)/Ru/RuO_(y) (0≦x≦1, 0≦y≦2), Ti/Ag/Cr,Ti/Ag/Ti/ITO, Ti/Ag/Cr/ITO, Ti/Ag/ITO, Ti/Ni/ITO, Ti/Rh, Ti/Ru, Rh,Rh/RhO₂, Ti/Ni/Al/ITO, Ti/Ni, Ti/W/Ti, W_(x)Ti_(1−z) (0≦x≦1),W_(x)Ti_(1−x)/Al(Cu) (0≦x≦1), W_(x)Ti_(1−x)/Al(Si) (0≦x≦1),W_(x)Ti_(1−x)/Al (0≦x≦1),Al, Al doped with Cu, Al doped with Mg, Aldoped with Si or Ti/Cu.

[0059] The further capacitor C_(B) is composed from a lower electrode 3,a dielectric 4, and an upper electrode. The lower electrode 5 of theresonator unit may be structured such that, for example, it also formsthe upper electrode of this capacitor.

[0060] The dielectric 4 of the capacitor CA may comprise, for example,SiO₂, Si₃N₄, Ta₂O₅ Si_(x)N_(y)O_(z) (0≦x≦1, 0≦y≦1, 0≦z≦1),SiO₂/Si₃N₄/SiO₂, Ba_(1−x)Sr_(x)TiO₃ (0≦x≦1), SrTi_(1−x)Zr_(x)O₃ (0≦x≦1)with or without Mn dopants, BaO—Ln₂O₃—TiO₂ (Ln=La. Ce, Nd, Sm or Eu),Al₂O₃, Ba₂Ti₉O₂₀, Ba₂Ti_(9−x)Zr_(x)O₂₀ (0≦x≦1) with or without Mndopants, BaTi₅O₁₁, BaTi₄O₉, Nb₂O₅, TiO₂, (Ta₂O₅)_(x)—(Al₂O₃)_(1−x)(0≦x≦1), (Ta₂O₅)_(x)—(TiO₂)_(1−x) (0≦x≦1), (Ta₂O₅)_(x)—(Nb₂O₅)_(1−x)(0≦x≦1), (Ta₂O₅)_(x)—(SiO₂)_(1−x) (0≦x≦1), (Sr,Ca)(Ti,Zr)O₃,BaO—SrO—Nd₂O₃—Gd₂O₃—Nb₂O₃—TiO₂, CaSm₂Ti₅O₁₄, Zr(Ti,Sn)O₄,BaO—PbO—CaO—Nd₂O₃—Pr₂O₃—Bi₂O₃—TiO₂, Ba(Zr,Zn,Ta)O₃, CaTiO₃—LaAlO₃,(Bi₃(Ni₂Nb)O₉)_(1−x)(Bi₂(ZnNb_(2(1+d)y)O_(3+6y+5yd))_(x) (0≦x≦1,0.5≦y≦1.5, −0.05≦d≦0.05), BiNbO₄ with or without dopants of VO_(x)(0≦x≦2.5), Ba(Zr,Ta)O₃, (Bi_(2−x)Zn_(x))(Zn_(2−y)Nb_(y))O₇ (0≦x≦1,0≦y≦1) or Bi₂(Zn_(⅓)Nb_(⅔))₂O₇. The lower electrode 3 may comprise, forexample, Ag_(1−x)Pt_(x) (0≦x≦1), Pt with a layer thickness from 50 nm to1 μm, Ti with a layer thickness from 1 to 20 nm/Pt with a layerthickness from 20 to 600 nm, Ti with a layer thickness from 1 to 20nm/Pt with a layer thickness from 20 to 600 nm/Ti with a layer thicknessfrom 1 to 20 nm, Pt with a layer thickness from 20 to 600 nm/Ti with alayer thickness from 1 to 20 nm, W, Ni, Mo, Au, Cu, Ti/Pt/Al, Ti/Ag,Ti/Ag/Ti, Ti/Ag/Ir, Ti/Ir, Ti/Pd, Ti/Ag_(1−x)Pt_(x) (0≦x≦1),Ti/Ag_(1−x)Pd_(x) (0≦x≦1), Ti/Pt_(1−x)Al_(x) (0≦x≦1), Pt_(1−x)Al_(x)(0≦x≦1), Ti/Ag/Pt_(1−x)Al_(x) (0≦x≦1), Ti/Ag/Ru, Ti/Ag/Ir/IrO_(x)(0≦x≦2), Ti/Ag/Ru/RuO_(x) (0≦x≦2), Ti/Ag/Ru/Ru_(x)Pt_(1−x) (0≦x≦1),Ti/Ag/Ru/Ru_(x)Pt_(1−x)/RuO_(y) (0≦x≦1, 0≦y≦2),Ti/Ag/Ru/RuO_(x)/Ru_(y)Pt_(1−y) (0≦x≦2, 0≦y≦1), Ti/Ag/Ru_(x)Pt_(1−x)(0≦x≦1), Ti/Ag/Pt_(x)Al_(1−x) (0≦x≦1), Pt_(x)Al_(1−x)/Ag/Pt_(y)Al_(1−y)(0≦x≦1, 0≦y≦1), Ti/Ag/Pt_(y)(RhO_(x))_(1−y) (0≦x≦2, 0≦y≦1),Ti/Ag/Rh/RhO_(x) (0≦x≦2), Ti/Ag/Pt_(x)Rh_(1−x) (0≦x≦1),Ti/Ag/Pt_(y)(RhO_(x))_(1−y)/Pt_(z)Rh_(1−z) (0≦x≦2, 0≦y≦1, 0≦z≦1),Ti/Ag_(x)Pt_(1−x)/Ir (0≦x≦1), Ti/Ag_(x)Pt_(1−x)/Ir/IrO_(y) (0≦x≦1,0≦y≦2), Ti/Ag_(x)Pt_(1−x)/Pt_(y)Al_(1−y) (0≦x≦1, 0≦y≦1),Ti/Ag_(x)Pt_(1−x)/Ru (0≦x≦1), Ti/Ag_(x)Pt_(1−x)/Ru/RuO_(y) (0≦x≦1,0≦y≦2), Ti/Ag/Cr, Ti/Ag/Ti/ITO, Ti/Ag/Cr/ITO, Ti/Ag/ITO, Ti/Ni/ITO,Ti/Rh, Ti/Ru, Rh, Rh/RhO₂, Ti/Ni/Al/ITO, Ti/Ni, Ti/W/Ti, W_(x)Ti_(1−x)(0≦x≦1), W_(x)Ti_(1−x)/Al(Cu) (0≦x≦1), W_(x)Ti_(1−x)/Al(Si) (0≦x≦1),W_(x)Ti_(1−x)/Al (0≦x≦1), Al, Al doped with Cu, Al doped with Si, Aldoped with Mg, or Ti/Cu.

[0061] Alternatively, the lower electrode of the capacitor CA and theupper electrode of the capacitor C_(B) may be formed through depositionof a separate electrically conducting layer.

[0062] A protective layer 10 of an organic or inorganic material, or acombination of these materials, may be provided over the entire filterarrangement. The organic material used may be, for example,polybenzocyclobutene or polyimide, and the inorganic material may be,for example, Si₃N₄, SiO₂, or Si_(x)O_(y)N_(z) (0≦x≦1, 0≦y≦1, 0≦z≦1).

[0063] Contact holes may be opened to the electrodes 3, 5, 7, and 9through the protective layer 10 by means of etching. Bump end contactsof Cr/Cu or Cr/Cu/Ni/Au may be grown in the contact holes. The contactto the filter input, to the filter output, and to ground may be effectedthrough these bump end contacts. In addition, a DC voltage in a range of1 to 100 V may be applied to the two electrodes 7, 9 of the capacitorC_(A), in dependence on the layer thickness of the dielectric 8.

[0064] The resonator unit and the capacitors can be electricallyinterconnected through vias in the piezoelectric layer 6 of theresonator unit and in the dielectric layers 4 and 8 of the capacitorsC_(A) and C_(B).

[0065] Alternatively, the reflection element 2 may comprise severallayers of high and low acoustic impedance in alternation, each layerhaving a layer thickness of one fourth the resonance wavelength λ. Thematerial of low acoustic impedance may be, for example, an organic orinorganic aerogel, an organic or inorganic xerogel, a glass foam, afoam-type adhesive, a foamed synthetic resin, a synthetic resin of lowdensity, or SiO₂. The material of high acoustic impedance may be, forexample, HfO₂, Mo, Au, Ni, Cu, W, Ti/W/Ti, W_(x)Ti_(1−x) (0≦x≦1),diamond, Ta₂O₅, AlN, Pt, Ti/Pt, or a synthetic resin of high densitysuch as, for example, high-density polyethylene (HDPE). It is alsopossible for the lower electrode 5 of the resonator to be at the sametime the upper layer of the λ/4 layers of the reflection element 2.

[0066] In a further embodiment of the invention, a second reflectionelement may be provided on the upper electrode 7 of the bulk acousticwave resonator.

[0067] A further alternative is to provide an additional adhesive layer,for example made of an acrylate glue or an epoxy glue, between thereflection element 2 and the substrate 1. The acrylate glue maycomprise, for example, acryl or methacryl monomers which polymerizeduring the curing process.

[0068] Furthermore, a layer of SiO₂ with a layer thickness of between 30and 300 nm may be provided above or below, or above and below areflection element 2 made of porous SiO₂. These SiO₂ layers, thereflection element 2, and a second reflection element may be providedover the entire region of the substrate 1 or only partly, in the regionof a resonator unit.

[0069] In addition, the entire filter arrangement may be provided withat least a first and a second current supply contact. The current supplycontact used may be, for example, an electroplated SME end contact ofCr/Cu, Ni/Sn, or Cr/Cu, Cu/Ni/Sn, or Cr/Ni, Pb/Sn, or Cr/Cu, Ni/Au, or abump end contact of Cr/Cu or Cr/Cu/Ni/Au, or a contact pad.

[0070] If so desired, an alternative type of bulk acoustic waveresonator such as, for example, a single-crystal resonator, a resonatorwith a membrane, or a resonator with an air gap may be used in thetunable filter arrangement, or a surface acoustic wave resonator with acorrespondingly adapted design of the electrodes 3, 5 and thepiezoelectric layer 4. It is also possible to use LC resonators whichare built up from coils and capacitors.

[0071] Alternative embodiments as to the construction and integrationare known to those skilled in the art. Thus, for example, a tunablefilter arrangement may comprise more than two resonators. It is alsopossible for two or more resonators to be connected to one capacitorwith tunable capacitance value in a tunable filter arrangement. If aresonator is connected to several capacitors, the latter may beconnected to the resonator in a wide variety of circuit arrangements.

[0072]FIG. 2 shows the circuit diagram of a tunable filter arrangement.This filter arrangement, which represents no more than one out of manypossible embodiments of the invention, comprises a series resonator R1and a parallel resonator R2 connected between a filter input 11 and afilter output 12. A capacitor C1 is connected in parallel to theresonator R1, while a further capacitor C2 is connected in seriesdownstream of the resonator R1. A capacitor C3 is connected downstreamin series with the parallel resonator R2, and a capacitor C4 isconnected in parallel to the resonator R2. The second terminal of theserial capacitor C3 is connected to ground. The capacitors C1 and C3have trimmable capacitance values.

[0073]FIG. 3 is a diagrammatic plan view of a filter arrangement with acircuit in accordance with FIG. 2 and a possible design of theelectrodes 3, 5, 7, and 9, the dielectrics 4 and 8, and thepiezoelectric layer 6.

[0074]FIG. 4 shows the filter curves of a tunable filter arrangement ofFIG. 2. Curve 13 here shows the filter characteristic of the filterarrangement without a DC voltage being applied to the electrodes of thecapacitors C1 and C3. Curve 14 shows the changed filter characteristicwhen a DC voltage of 5 V is applied to the capacitors C1 and C3.

[0075] Embodiments of the invention will be explained in more detailbelow, representing examples of how the invention may be realized inpractice.

[0076] Embodiment 1

[0077] An adhesive layer of an acrylate glue is present on a substrate 1of glass, and thereon are arranged a 300 nm thick layer of SiO₂, areflection element 2 of porous SiO₂, and a 30 nm thick layer of SiO₂. Anelectrode 5 of Pt/Ti is present en the 30 nm thick SiO₂ layer. Apiezoelectric layer 6 of PbZr_(0.35)Ti₀ ₆₅O₃ lies on the electrode 5,and an electrode 7 of Ti/Pt is present on the piezoelectric layer 6. Thepiezoelectric layer 6 and the two electrodes 5, 7 are deposited andstructured such that a filter arrangement with a series resonator R1 anda parallel resonator R2 are created. The electrode 5 is deposited andstructured such that it also forms the upper electrode of a capacitor C4adjacent the resonator R2. The electrode 7 is deposited and structuredsuch that it forms the lower electrode of a capacitor C1 as well as theupper electrode of a capacitor C2 in the region of the bulk acousticwave resonator R2, and forms the lower electrode of a capacitor C3 inthe region of the bulk acoustic wave resonator R2. A dielectric 8 ofPbZr_(0.53)Ti_(0.47)O₃ with 5% lanthanim doping lies on the lowerelectrodes 7 of the capacitors C1 and C3, and an upper electrode 9 ofPt/Ti is provided on the respective dielectrics 8. The capacitors C2 andC4 each comprise besides an upper electrode of Pt/Ti a dielectric 4 ofSi₃N₄ and a lower electrode 3 of Al doped with 4% Cu.

[0078] A protective layer 10 of SiO₂ is provided over the entire filterarrangement. Contact holes are etched through the protective layer 10 tothe electrodes 3, 5, 7, and 9. Bump end contacts of Cr/Cu/Ni/Au aregrown in the contact holes.

[0079] A bump end contact to the electrode 5 in the region of theresonator R1 serves as a contact to the filter input 11 of the filterarrangement, and a bump end contact to the electrode 3 in the region ofthe capacitor R2 serves as a contact for the filter output 12 of thefilter arrangement. In addition, a bump end contact to the electrode 9in the region of the capacitor C3 is connected to ground.

[0080] The capacitors C1, C2, C3, and C4 and the resonators R1 and R2are electrically interconnected through suitable vias in thepiezoelectric layer 6, the dielectric 8, and the dielectric 4. Thecapacitor C1 is connected in parallel to the resonator R1, whereas thecapacitor C2 is connected in series downstream of the resonator R1. Thecapacitor C3 is connected in series downstream of the resonator R2, andthe capacitor C4 is connected in parallel to the resonator R2.

[0081] The two resonators R1 and R2 are mutually attuned such that theresonance frequency of the resonator R1 corresponds to theanti-resonance frequency of the resonator R2. The filter characteristicof the filter arrangement can be changed through the application of a DCvoltage to the capacitors C1 and C3, because the relative dielectricconstant ε_(r) of the material of the dielectric 8 is changed thereby.The application of a DC voltage of a few volts is capable of reducingthe capacitance values of the capacitors C1 and C3 by up to a factor 10.As a result, the resonance frequencies and the anti-resonancefrequencies of the resonators R1 and R2 are shifted, and the filtercurve of the filter arrangement is shifted by a few percents. The DCvoltage is applied to the electrodes 7 and 9 of the capacitors C1 and C3through the bump end contacts.

[0082]FIG. 4 shows an example of such a shift. The series resonator R1has a resonance frequency of 1 GHz, and the parallel resonator R2 has aresonance frequency of 0.95035 GHz. The four capacitors without a DCvoltage applied to the electrodes of the capacitors C1 and C3 have thefollowing capacitance values: C1=2 pF, C2=100 pF, C3=100 pF, and C4=10pF. The filter characteristic of this filter arrangement is shown incurve 13. After a DC voltage of 20 V has been applied, the capacitancevalues of C1 and C3 are reduced by the factor 10, and the bandwidth ofthe filter is shifted to higher frequencies. Curve 14 corresponds tothis new filter characteristic.

[0083] The resulting filter arrangement was used in mobile telephones asa tunable bandpass filter whose filter band can be changed.

[0084] Embodiment 2

[0085] An adhesive layer of an acrylate glue is present on a substrate 1of glass, and thereon are arranged a 300 nm thick layer of SiO₂, areflection element 2 of porous SiO₂, and a 30 nm thick layer of SiO₂. Anelectrode 5 of Pt/Ti is present on the 30 nm thick SiO₂ layer. Apiezoelectric layer 6 of AlN lies on the electrode 5, and an electrode 7of Ti/Pt is present on the piezoelectric layer 6. The piezoelectriclayer 6 and the two electrodes 5, 7 are deposited and structured suchthat a filter arrangement with a series resonator R1 and a parallelresonator R2 are created. The electrode 5 is deposited and structuredsuch that it also forms the upper electrode of a capacitor C4 adjacentthe resonator R2. The electrode 7 is deposited and structured such thatit forms the lower electrode of a capacitor C I as well as the upperelectrode of a capacitor C2 in the region of the bulk acoustic waveresonator R2, and forms the lower electrode of a capacitor C3 in theregion of the bulk acoustic wave resonator R2. A dielectric 8 ofPbZr_(0.53)Ti_(0.47)O₃ with 5% lanthanum doping lies on the lowerelectrodes 7 of the capacitors C I and C3, and an upper electrode 9 ofPt/Ti is provided on the respective dielectrics 8. The capacitors C2 andC4 each comprise besides an upper electrode of Pt/Ti a dielectric 4 ofSi₃N₄ and a lower electrode 3 of Al doped with 4% Cu.

[0086] A protective layer 10 of SiO₂ is provided over the entire filterarrangement. Contact holes are etched through the protective layer 10 tothe electrodes 3, 5, 7, and 9. Bump end contacts of Cr/Cu/Ni/Au aregrown in the contact holes.

[0087] A bump end contact to the electrode 5 in the region of theresonator R1 serves as a contact to the filter input 11 of the filterarrangement, and a bump end contact to the electrode 3 in the region ofthe capacitor R2 serves as a contact for the filter output 12 of thefilter arrangement. In addition, a bump end contact to the electrode 9is connected to ground in the region of the capacitor C3.

[0088] The capacitors C1, C2, C3, and C4 and the resonators R1 and R2are electrically interconnected through suitable vias in thepiezoelectric layer 6, the dielectric 8, and the dielectric 4. Thecapacitor C1 is connected in parallel to the resonator R1, whereas thecapacitor C2 is connected in series downstream of the resonator R1. Thecapacitor C3 is connected in series downstream of the resonator R2, andthe capacitor C4 is connected in parallel to the resonator R2.

[0089] The two resonators R1 and R2 are mutually attuned such that theresonance frequency of the resonator R1 corresponds to theanti-resonance frequency of the resonator R2. The filter characteristicof the filter arrangement can be changed through the application of a DCvoltage to the capacitors C1 and C3, because the relative dielectricconstant ε_(r) of the material of the dielectric 8 is changed thereby.The application of a DC voltage of a few volts is capable of reducingthe capacitance values of the capacitors C1 and C3 by up to a factor 10.As a result, the resonance frequencies and the anti-resonancefrequencies of the resonators R1 and R2 are shifted, and the filtercurve of the filter arrangement is shifted by a few percents. The DCvoltage is applied to the electrodes 7 and 9 of the capacitors C1 and C3through the bump end contacts.

[0090] The resulting filter arrangement was used in mobile telephones asa tunable bandpass filter whose filter band can be changed.

[0091] Embodiment 3

[0092] A reflection element 2 of alternating λ/4 layers of AlN and SiO₂is present on a substrate 1 of glass. An electrode 5 of Pt/Ti lies onthe reflection element 2. A piezoelectric layer 6 of AlN is present onthe electrode 5, and an electrode 7 of Pt/Ti lies on the piezoelectriclayer 6. The piezoelectric layer 6 and the two electrodes 5, 7 aredeposited and structured such that a filter arrangement with a seriesresonator R1 and a parallel resonator R2 are created. The electrode 5 isdeposited and structured such that it also forms the upper electrode ofa capacitor C4 adjacent the resonator R2. The electrode 7 is depositedand structured such that it forms the lower electrode of a capacitor C1as well as the upper electrode of a capacitor C2 in the region of thebulk acoustic wave resonator R2, and forms the lower electrode of acapacitor C3 in the region of the bulk acoustic wave resonator R2. Adielectric 8 of PbZr_(0.53)Ti_(0.47)O₃ with 5% lanthanum doping lies onthe lower electrodes 7 of the capacitors C1 and C3, and an upperelectrode 9 of Pt/Ti is provided on the respective dielectrics 8. Thecapacitors C2 and C4 each comprise besides an upper electrode of Pt/Ti adielectric 4 of Si₃N₄ and a lower electrode 3 of Al doped with 4% Cu.

[0093] A protective layer 10 of Si₃N₄ is provided over the entire filterarrangement. Contact holes are etched through the protective layer 10 tothe electrodes 3, 5, 7, and 9. Bump end contacts of Cr/Cu/Ni/Au aregrown in the contact holes.

[0094] A bump end contact to the electrode 5 in the region of theresonator R1 serves as a contact to the filter input 11 of the filterarrangement, and a bump end contact to the electrode 3 in the region ofthe capacitor R2 serves as a contact for the filter output 12 of thefilter arrangement. In addition, a bump end contact to the electrode 9is connected to ground in the region of the capacitor C3.

[0095] The capacitors C1, C2, C3, and C4 and the resonators R1 and R2are electrically interconnected through suitable vias in thepiezoelectric layer 6, the dielectric 8, and the dielectric 4 of thecapacitor C4. The capacitor C1 is connected in parallel to the resonatorR1, whereas the capacitor C2 is connected in series downstream of theresonator R1. The capacitor C3 is connected in series downstream of theresonator R2, and the capacitor C4 is connected in parallel to theresonator R2.

[0096] The two resonators R1 and R2 are mutually attuned such that theresonance frequency of the resonator R1 corresponds to theanti-resonance frequency of the resonator R2. The filter characteristicof the filter arrangement can be changed through the application of a DCvoltage to the capacitors C1 and C3, because the relative dielectricconstant ε_(r) of the material of the dielectric 8 is changed thereby.The application of a DC voltage of a few volts is capable of reducingthe capacitance values of the capacitors C1 and C3 by up to a factor 10.As a result, the resonance frequencies and the anti-resonancefrequencies of the resonators R1 and R2 are shifted, and the filtercurve of the filter arrangement is shifted by a few percents. The DCvoltage is applied to the electrodes 7 and 9 of the capacitors C1 and C3through the bump end contacts.

[0097] The resulting filter arrangement was used in mobile telephones asa tunable bandpass filter whose filter band can be changed.

[0098] Embodiment 4

[0099] A reflection element 2 of alternating λ/4 layers of Ta₂O₅ andSiO₂ is present on a substrate 1 of glass. An electrode 5 of Pt/Ti lieson the reflection element 2. A piezoelectric layer 6 of AlN is presenton the electrode 5, and an electrode 7 of Pt/Ti lies on thepiezoelectric layer 6. The piezoelectric layer 6 and the two electrodes5, 7 are deposited and structured such that a filter arrangement with aseries resonator R1 and a parallel resonator R2 are created. Theelectrode 5 is deposited and structured such that it also forms theupper electrode of a capacitor C4 adjacent the resonator R2. Theelectrode 7 is deposited and structured such that it forms the lowerelectrode of a capacitor C1 as well as the upper electrode of acapacitor C2 in the region of the bulk acoustic wave resonator R2, andforms the lower electrode of a capacitor C3 in the region of the bulkacoustic wave resonator R2. A dielectric 8 of PbZr_(0.53)Ti_(0.47)O₃with 5% lanthanum doping lies on the lower electrodes 7 of thecapacitors C1 and C3, and an upper electrode 9 of Pt/Ti is provided onthe respective dielectrics 8. The capacitors C2 and C4 each comprisebesides an upper electrode of Pt/Ti a dielectric 4 of Si₃N₄ and a lowerelectrode 3 of Al doped with 4% Cu.

[0100] A protective layer 10 of Si₃N₄ is provided over the entire filterarrangement. Contact holes are etched through the protective layer 10 tothe electrodes 3, 5, 7, and 9. Bump end contacts of Cr/Cu/Ni/Au aregrown in the contact holes.

[0101] A bump end contact to the electrode 5 in the region of theresonator R1 serves as a contact to the filter input 11 of the filterarrangement, and a bump end contact to the electrode 3 in the region ofthe capacitor R2 serves as a contact for the filter output 12 of thefilter arrangement. In addition, a bump end contact to the electrode 9is connected to ground in the region of the capacitor C3.

[0102] The capacitors C1, C2, C3, and C4 and the resonators R1 and R2are electrically interconnected through suitable vias in thepiezoelectric layer 6, the dielectric 8, and the dielectric 4. Thecapacitor C1 is connected in parallel to the resonator R1, whereas thecapacitor C2 is connected in series downstream of the resonator R1. Thecapacitor C3 is connected in series downstream of the resonator R2, andthe capacitor C4 is connected in parallel to the resonator R2.

[0103] The two resonators R1 and R2 are mutually attuned such that theresonance frequency of the resonator R1 corresponds to theanti-resonance frequency of the resonator R2. The filter characteristicof the filter arrangement can be changed through the application of a DCvoltage to the capacitors C1 and C3, because the relative dielectricconstant ε_(r) of the material of the dielectric 8 is changed thereby.The application of a DC voltage of a few volts is capable of reducingthe capacitance values of the capacitors C1 and C3 by up to a factor 10.As a result, the resonance frequencies and the anti-resonancefrequencies of the resonators R1 and R2 are shifted, and the filtercurve of the filter arrangement is shifted by a few percents. The DCvoltage is applied to the electrodes 7 and 9 of the capacitors C1 and C3through the bump end contacts.

[0104] The resulting filter arrangement was used in mobile telephones asa tunable bandpass filter whose filter band can be changed.

[0105] Embodiment 5

[0106] A reflection element 2 with alternating λ/4 layers of Ta₂O₅ andSiO₂ is present on a silicon substrate I with a passivating layer ofSiO₂. An electrode 5 of Ti/Pt lies on the reflection element 2. Apiezoelectric layer 6 of AlN lies on the electrode 5, and an electrode 7of Ti/Pt lies on the piezoelectric layer 6. The piezoelectric layer 6and the two electrodes 5, 7 are deposited and structured such that afilter arrangement with a series resonator R1 and a parallel resonatorR2 are created. The electrode 5 is deposited and structured such that italso forms the upper electrode of a capacitor C4 adjacent the resonatorR2. The electrode 7 is deposited and structured such that it forms thelower electrode of a capacitor C1 as well as the upper electrode of acapacitor C2 in the region of the bulk acoustic wave resonator R2, andforms the lower electrode of a capacitor C3 in the region of the bulkacoustic wave resonator R2. A dielectric 8 of PbZr_(0.53)Ti_(0.47)O₃with 5% lanthanum doping lies on the lower electrodes 7 of thecapacitors C1 and C3, and an upper electrode 9 of Pt/Ti is provided onthe respective dielectrics 8. The capacitors C2 and C4 each comprisebesides an upper electrode of Pt/Ti a dielectric 4 of Si₃N₄ and a lowerelectrode 3 of Ti/Pt.

[0107] A protective layer 10 of Si₃N₄ is provided over the entire filterarrangement. Contact holes are etched through the protective layer 10 tothe electrodes 3, 5, 7, and 9. Bump end contacts of Cr/Cu/Ni/Au aregrown in the contact holes.

[0108] A bump end contact to the electrode 5 in the region of theresonator R1 serves as a contact to the filter input 11 of the filterarrangement, and a bump end contact to the electrode 3 in the region ofthe capacitor R2 serves as a contact for the filter output 12 of thefilter arrangement. In addition, a bump end contact to the electrode 9is connected to ground in the region of the capacitor C3.

[0109] The capacitors C1, C2, C3, and C4 and the resonators R1 and R2are electrically interconnected through suitable vias in thepiezoelectric layer 6, the dielectric 8, and the dielectric 4. Thecapacitor C1 is connected in parallel to the resonator R1, whereas thecapacitor C2 is connected in series downstream of the resonator R1. Thecapacitor C3 is connected in series downstream of the resonator R2, andthe capacitor C4 is connected in parallel to the resonator R2.

[0110] The two resonators R1 and R2 are mutually attuned such that theresonance frequency of the resonator R1 corresponds to theanti-resonance frequency of the resonator R2. The filter characteristicof the filter arrangement can be changed through the application of a DCvoltage to the capacitors C I and C3, because the relative dielectricconstant ε_(r) of the material of the dielectric 8 is changed thereby.The application of a DC voltage of a few volts is capable of reducingthe capacitance values of the capacitors C1 and C3 by up to a factor 10.As a result, the resonance frequencies and the anti-resonancefrequencies of the resonators R1 and R2 are shifted, and the filtercurve of the filter arrangement is shifted by a few percents. The DCvoltage is applied to the electrodes 7 and 9 of the capacitors C1 and C3through the bump end contacts.

[0111] The resulting filter arrangement was used in mobile telephones asa tunable bandpass filter whose filter band can be changed.

[0112] Embodiment 6

[0113] A reflection element 2 with alternating λ/4 layers of Ta₂O₅ andSiO₂ is present on a silicon substrate 1 with a passivating layer ofSiO₂. An electrode 5 of Ti/Pt lies on the reflection element 2. Apiezoelectric layer 6 of AlN lies on the electrode 5, and an electrode 7of Ti/Pt lies on the piezoelectric layer 6. The piezoelectric layer 6and the two electrodes 5, 7 are deposited and structured such that afilter arrangement with a series resonator R1 and a parallel resonatorR2 are created. The electrode 5 is deposited and structured such that italso forms the upper electrode of a capacitor C4 adjacent the resonatorR2. The electrode 7 is deposited and structured such that it forms thelower electrode of a capacitor C1 as well as the upper electrode of acapacitor C2 in the region of the bulk acoustic wave resonator R2, andforms the lower electrode of a capacitor C3 in the region of the bulkacoustic wave resonator R2. A dielectric 8 of PbZr_(0.53)Ti_(0.47)O₃with 5% lanthanum doping lies on the lower electrodes 7 of thecapacitors C1 and C3, and an upper electrode 9 of Pt/Ti is provided onthe respective dielectrics 8. The capacitors C2 and C4 each comprisebesides an upper electrode of Pt/Ti a dielectric 4 of Si₃N₄ and a lowerelectrode 3 of Al doped with 4% Cu, which is separately deposited.

[0114] A protective layer 10 of Si₃N₄ is provided over the entire filterarrangement. Contact holes are etched through the protective layer 10 tothe electrodes 3, 5, 7, and 9. Bump end contacts of Cr/Cu/Ni/Au aregrown in the contact holes.

[0115] A bump end contact to the electrode 5 in the region of theresonator R1 serves as a contact to the filter input 11 of the filterarrangement, and a bump end contact to the electrode 3 in the region ofthe capacitor R2 serves as a contact for the filter output 12 of the ailfilter arrangement. In addition, a bump end contact to the electrode 9is connected to ground in the region of the capacitor C3.

[0116] The capacitors C1, C2, C3, and C4 and the resonators R1 and R2are electrically interconnected through suitable vias in thepiezoelectric layer 6, the dielectric 8, and the dielectric 4. Thecapacitor C1 is connected in parallel to the resonator R1, whereas thecapacitor C2 is connected in series downstream of the resonator R1. Thecapacitor C3 is connected in series downstream of the resonator R2, andthe capacitor C4 is connected in parallel to the resonator R2.

[0117] The two resonators R1 and R2 are mutually attuned such that theresonance frequency of the resonator R1 corresponds to theanti-resonance frequency of the resonator R2. The filter characteristicof the filter arrangement can be changed through the application of a DCvoltage to the capacitors C1 and C3, because the relative dielectricconstant ε_(r) of the material of the dielectric 8 is changed thereby.The application of a DC voltage of a few volts is capable of reducingthe capacitance values of the capacitors C1 and C3 by up to a factor 10.As a result, the resonance frequencies and the anti-resonancefrequencies of the resonators R1 and R2 are shifted, and the filtercurve of the filter arrangement is shifted by a few percents. The DCvoltage is applied to the electrodes 7 and 9 of the capacitors C1 and C3through the bump end contacts.

[0118] The resulting filter arranged was used in mobile telephones as atunable bandpass filter whose filter band can be changed.

1. A tunable filter arrangement which comprises a substrate (1) andprovided thereon an arrangement of at least two mutually coupledresonators of which at least one is connected to a capacitor withtunable capacitance.
 2. A tunable filter arrangement as claimed in claim1 , characterized in that the capacitor comprises a dielectric (8) madeof a material having EL voltage-dependent relative dielectric constantε_(r).
 3. A tunable filter arrangement as claimed in claim 2 ,characterized in that the material with a voltage-dependent relativedielectric constant ε_(r) is chosen from the group comprisingPbTi_(1−x)Zr_(x)O₃ (0≦x≦1) with and without dopants of La, Nb or Mn withand without excess lead, BaTiO₃ with and without dopants, SrTiO₃ withand without dopants, Ba_(1−x)Sr_(x)TiO₃ (0≦x≦1) with and without dopantsof Ca and Pb, Ba_(1−x)Sr_(x)TiO₃ (0≦x≦1)+MgO,Ba_(1−x)Sr_(x)TiO₃—Pb_(1−y)Ca_(y)TiO₃ (0≦x≦1, 0≦y≦1), CaTiO₃ doped withBi, Sr_(n+1)Ti_(n)O_(3n+1) (1≦n≦5), Pb_(1−x)Ca_(x)TiO₃ (0≦x≦1),Ba_(1−x)Sr_(x)TiO₃ (0≦x≦1) with and without added VO_(x) (1≦x≦2.5)and/or SiO₂, Ba_(1−x)Sr_(x)Zr_(y)Ti_(1−y)O₃ (0≦x≦1, 0≦y≦1) with andwithout dopants, Ba_(1−x)Pb_(x)TiO₃ (0≦x≦1) with and without excesslead, Ba_(1−x)Ca_(x)TiO₃ (0≦x≦1), SrZr_(x)Ti_(1−x)O₃ (0≦x≦1) with andwithout dopants, [PbMg_(⅓)Nb_(⅔)O₃]_(x)—[PbTiO₃]_(1−x) (0≦x≦1),(Pb,Ba,Sr)(Mg_(⅓)Nb_(⅔))_(x)Ti_(y)(Zn_(⅓)Nb_(⅔))_(1−x-y)O₃ (0≦x≦1,0≦y≦1), Pb_(1−x)Ca_(x)TiO₃ (0≦x≦1),(Ba_(1−x+y/8)Sr_(x+y/8))₂Na_(1−y)Nb₅O₁₅ (0≦x≦1, 0≦y≦1) with and withoutexcess Na⁺, (Ba_(1−x+y/8)Sr_(x+y/8))₂K_(1−y) Nb₅O₁₅ (0≦x≦1, 0≦y≦1) withand without excess K⁺, (Ba_(1−x)Sr_(x))₂K_(1−3y)SE_(y)Nb₅O₁₅ (0≦x≦1,0≦y≦1, SE=ion from the group of rare earths), Sr₂Ba₄Ti₂Nb₈O₃₀, BiNbO₄with and without VO_(x) (1≦x≦2.5) and/or CuO dopants,(Bi_(2−x)Zn_(x))(Nb_(2−y)Zn_(y))O_(x), Bi₂(Zn_(⅓)Nb_(⅔))₂O₇, a)Pb(Mg_(½)WI_(½))O₃, b) Pb(Fe_(½)Nb_(½))O₃, c) Pb(Fe_(⅔)WI_(⅓))O₃, d)Pb(Ni_(⅓)Nb_(⅔))O₃, e) Pb(Zn_(⅓)Nb_(⅔))O₃, f) Pb(Sc_(½)Ta_(½))O₃,combinations of the compounds a) to f) with PbTiO₃ and/orPb(Mg_(⅓)Nb_(⅔))O₃ with and without excess lead and Ba_(1−x)Zr_(x)TiO₃(0≦x≦1).
 4. A tunable filter arrangement as claimed in claim 1 ,characterized in that the resonators are chosen from the groupcomprising bulk acoustic wave resonators, surface acoustic waveresonators, and LC resonators.
 5. A tunable filter arrangement asclaimed in claim 4 , characterized in that the resonators areconstructed in a thin-film technology process.
 6. A tunable filterarrangement as claimed in claim 4 , characterized in that a bulkacoustic wave resonator comprises a resonator unit of a lower and anupper electrode (5, 7) as well as a piezoelectric layer (6) arrangedtherebetween and a reflection element (2) arranged between the substrate(1) and the resonator unit.
 7. A tunable filter arrangement as claimedin claim 1 , characterized in that the resonator connected to acapacitor of tunable capacitance is also connected to a furthercapacitor.
 8. A tunable filter arrangement as claimed in claim 7 ,characterized in that at least one capacitor is connected in series withand at least one capacitor is connected in parallel to the resonator. 9.A mobile telephone device provided with a tunable filter arrangementwhich comprises a substrate and provided thereon an arrangement of atleast two mutually coupled resonators of which at least one is connectedto a capacitor with tunable capacitance.
 10. A transmitter provided witha tunable filter arrangement which comprises a substrate and providedthereon an arrangement of at least two mutually coupled resonators ofwhich at least one is connected to a capacitor with tunable capacitance.11. A receiver provided with a tunable filter arrangement whichcomprises a substrate and provided thereon an arrangement of at leasttwo mutually coupled resonators of which at least one is connected to acapacitor with tunable capacitance.
 12. A wireless data transmissionsystem provided with a tunable filter arrangement which comprises asubstrate and provided thereon an arrangement of at least two mutuallycoupled resonators of which at least one is connected to a capacitorwith tunable capacitance.
 13. A tunable bulk acoustic wave resonatorwhich comprises a substrate and provided thereon a resonator unit with alower and an upper electrode as well as a piezoelectric layer arrangedtherebetween, and a reflection element which is arranged between thesubstrate and the resonator unit, which resonator is connected to acapacitor having a tunable capacitance value.